Temperature compensated fluid sensor

ABSTRACT

There is described an improved apparatus for detecting the presence or absence of fluid. The apparatus comprises an electrical circuit and a sensor device electrically joined to the circuit. The device comprises a housing member defining a chamber, a thermally conductive member within the chamber, a tip member forming a closure for the chamber, a heater means within said chamber having first and second spaced apart portions, and first and second heat responsive members respectively affixed to the spaced apart portions and adapted for engaging when the temperature difference between the portions exceeds a predetermined level. The improvement comprises providing a secondary heater means assuring continuous electrical engagement between one of the heat responsive members and the second spaced apart portion of the heater means as long as the previously described temperature difference exists.

llnited Sta es atent [191 Bickmire et al.

[ Apr. 9, 1974 TEMPERATURE COMPENSATED FLUID SENSOR [75] Inventors: Walter W. Bickmire; Nikolaus A.

Szeverenyi; David F. Thompson, all of Warren, Pa.

[73] Assignee: GTE Sylvania Incorporated, Seneca Falls, N.Y.

221 Filed: Nov. 2, 1972 21 Appl.No.:303,245

Primary Examiner-George Harris Attorney, Agent, or FirmNorman J. OMalley; Donald R. Castle; Wm. H. McNeill [5 7] ABSTRACT There is described an improved apparatus for detecting the presence or absence of fluid. The apparatus comprises an electrical circuit and a sensor device electrically joined to the circuit. The device comprises a housing member defining a chamber, a thermally conductive member within the chamber, a tip member forming a closure for the chamber, a heater means within said chamber having first and second spaced apart portions, and first and second heat responsive members respectively affixed to the spaced apart portions and adapted for engaging when the temperature difference between the portions exceeds a predetermined level. The improvement comprises providing a secondary heater means assuring continuous electrical engagement between one of the heat responsive members and the second spaced apart portion of the heater means as long as the previously described temperature difference exists.

7 Claims, 7 Drawing Figures PATENTEDAPR- 9 I974 3. 803. 525

SHEET 1 [IF 2 CROSS REFERENCE TO CO-PENDING APPLICATIONS A previous patent application U.S. Ser. No. 236,148, filed Mar. 20, 1972 discloses and claims a sensing apparatus and device and is assigned to the same assignee of the present invention. The present application comprises an improvement to this apparatus and device. The present invention provides in the device a secondary heater means to achieve a continuous electrical connection between the first heat responsive means and the second spaced apart portion of the heater means of the device when the described temperature difference between the spaced apart portions of the heater means attains the described predetermined level. This secondary heater means is not provided in the device of the cited application.

BACKGROUND OF THE INVENTION This invention relates to fluid sensing apparatus and more particularly to an apparatus for providing an indication when said fluid approaches a predetermined level.

Previous known methods for detecting fluid have varied from mechanically operated floats to probing devices requiring elaborate electronic circuitry. A particular shortcoming to many devices of the former variety has been the inability to compensate for a change in temperature of the fluid being measured. Additionally, those devices able to compensate for fluid temperature changes have, as mentioned, required extensive electronic circuitry which in turn has added appreciably to the complexity of operation of the device as well as to the costs for manufacturing such items.

It is believed, therefore, that a device for detecting the presence or absence of fluid at a predetermined level within a container which would compensate for varying temperatures of the fluid being measured as well as be relatively simple in operation and inexpensive to manufacture would constitute an advancement in the art.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a primary object of this invention to provide a fluid sensing apparatus which includes a means for compensating for possible varying temperatures of the fluid to be detected.

It is a further object of this invention to provide a sensing apparatus which operates in a relatively simple manner and is relatively inexpensive to manufacture.

It is a still further object of this invention to provide a fluid sensing apparatus which provides a continuously steady indication upon detection of such fluid.

In accordance with one aspect of this invention there is'provided an improved apparatus for detecting the presence or absence of fluid at a predetermined level within a container. This apparatus comprises an electrical circuit having a potential source, a switching means for opening and closing the circuit, and a current indicating means for indicating when the current in the circuit exceeds an established level. Additionally, the apparatus comprises a sensor device electrically connected to the circuit and having a housing, a thermally conducting member positioned within the housing and insulated therefrom, a tip member bonded to the housing, a resistive element having first and second opposing ends of conductive material, and first and second oppositely aligned bimetallic members possessing a substantially similar degree of thermal deflection and affixed respectively to the first and second opposing ends of the resistive element. These bimetallic members are adapted for engaging when the temperature difference between the opposing ends of the resistive element exceeds a predetermined level. The improvement to this apparatus comprises a means for assuring continuous engagement of the bimetallic members as long as the previously described temperature difference exists.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. l is a side elevational view of one embodiment of the present invention.

FIG. 2 is an enlarged FIG. 1.

FIGS. 3 and 4 are enlarged views of various phases of operation of the sensor of FIG. 2.

FIG. 5 is an enlarged plan view of the heat responsive members of the sensor device as taken along the line 55 in FIG. 4.

FIG. 6 is an isometric view illustrating another embodiment of a means for providing continuous engagement of the heat responsive members.

FIG. 7 is a side elevational view illustrating still another embodiment of a means for providing continuous engagement of the heat responsive members.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the aforedescribed drawings.

In FIG. 1 one embodiment of a fluid detecting apparatus 10 in accordance with the invention is illustrated and shown to comprise an electrical circuit Ill and a sensor device 13. Circuit 11 comprises a potential source illustrated as battery 15, a switching means 117 for opening and closing cirucit 11, and a current indicating means, illustrated as bulb l9. Sensor device 113 is electronically connected to circuit 111 and is shown to be positioned within wall 21 of a fluid holding container 23. Although the particular method illustrated for positioning sensor 13 is to place it in the side of container 23, sensor 13 may be placed in either the bottom or top of the container depending on the level of fluid desired or the configuration of the container. Furthermore, although the method shown for retaining sensor 13 in wall 211 is by screw threads (the sensor being pro-' vided with external screw threads to mate with corresponding threads in wall 21), other methods for retention are possible, an example being either welding or soldering. The method illustrated is preferred, however, because it provides relative ease of removal of sensor 13 in the event of damage to the sensor or container.

In FIG. 2 can be seen a more detailed view of sensor 113, which is shown to comprise a housing 25 of electrically conductive material, a thermally conducting member, illustrated as center post 27, which is positioned within housing 25 and insulated therefrom by insulating material 29, a heater means illustrated as a view of the sensor device of resistive element 31, and a tip member 33 of electrically conductive material. Center post 27 is preferably also electrically conductive and is connected to circuit 11 via plug 35 illustrated as a body of insulative material 37 about a metallic socket 39 which in turn is connected to conducting wire 41. Plug 35 is but one means possible for providing this interconnection and is not meant as the sole method to which the invention limited. Additional connecting means, including an alligator clip or even a single wire soldered to post 27 are possible. In the event that the atmosphere surrounding container 23 is not favorable for exposed electrical connections, a plug having an insulating cap to encompass the external portions of either post 27 or housing 25 is preferred.

Tip member 33, sealed in housing 25 to thereby encapsulate resistive element 31 therein, is adapted for being subjected to the fluid within container 23. A preferred material for tip member 33 is sold under the trade name Rodar and manufactured by the W. B. Driver Company of Newark, New Jersey, a subsidiary of the assignee of the proposed present invention. Rodar, consisting essentially of about 29 percent by weight nickel, l7 percent by weight cobalt, and the remainder iron, is a suitable electrical conductor and possesses the additional property of relatively low thermal conductivity. This additional property, as will be further explained, is highly deisrable to enhance the functioning characteristics of sensor 13. Resistive element 31, comprising first and second opposing ends 43 and 45 respectively, is joined at first opposing end 43 to center post 27 and at second opposing end 45 to tip member 33. First and second opposing ends 43 and 45 are of electrically conductive material and have first and second heat responsive means 47 and 49 affixed respectively thereto. The conductive material preferred for opposing ends 43 and 45 is a nickel-silver metallic alloy, although any of the well known metals or metal alloys having good electrical conducting properties can be utilized.

Heat responsive means 47 and 49, illustrated as a pair of bimetallic members, possess similar electrical conducting properties and are illustrated as being oppositely aligned and in a non-engaging relationship when the fluid level in container 23 is above tip member 33. As will be explained, these bimetallic members are adapted for engaging when the fluid level drops below the tip member. Electrical connection between circuit 11 and housing 25 is accomplished simply by affixing a wire from circuit 11 to any external portion of the housing, using any of the conventional methods, for example, welding. In the event that container 23 is of metallic nature or any material having good electrical conducting properties, circuit 11 may be connected thereto at any suitable location.

To explain the operation of apparatus 10, particular reference is made to FIGS. 3 and 4. In FIG. 3, tip member 33 is shown to be subjected to the fluid within container 23. As previously explained, bimetallic members 47 and 49 are in a nonengaging relationship when these members are at the same temperature. These members are comprised ofa suitable bimetal having similar electrical conductive properties as well as similar degrees of thermal deflection thereby permitting each member to deflect substantially equal, as the environmental temperature alters. A unique feature of sensor device 13 is its ability to operate in fluids having a wide variety of temperatures, due to the positioning of bimetallic members 47 and 49. When the fluid surrounding tip member 33 is excessively warm, expandable members 47 and 49 deflect equally to the position illustrated in FIG. 3. In the event that the fluid is cooled, these members deflect accordingly in the opposite direction (shown in phantom). It is remembered, however, that members 47 and 49 maintain a non-engaging relationship throughout these varying stages of deflection, provided tip member 33 is subjected to the fluid within the container thereby keeping the temperature of all elements within the sensor substantially equal.

To operate apparatus 10, switching means 17 is closed, thereby providing electrical current to circuit 11 and to sensor 13. A typical direction of current flow from battery 15 is through center post 27, first opposing end 43 of resistive element 31, resistive material 51 of element 31, tip member 33, housing 25 and thereafter back to circuit 11 where it passes through bulb 19. Because this current must pass through resistive material 51, which may be any material typically found in electrical resistors, it is not sufficient to activate bulb 19. Assuring that bulb 19 will not light under these conditions is easily accomplished by proper selection of corresponding elements in the sensor and circuit. One example of a workable circuit-sensor arrangement is to use a 12 volt battery connected to a bulb having a resistance of approximately 1 ohm. When using this combination, the desired resistance of the resistive material of element 31 is approximately 240 ohms. The resistance of other elements in sensor 13, particularly housing 25, opposing ends 43 and 45, center post 27, tip member 33, and bimetallic members 47 and 49 is minimal and can be considered effectively as zero.

The current through resistive material 51 causes this material to become warm as is the case in almost all electrical resistors. This heat then dissipates out through opposing ends 43 and 45 of element 31. The heat dissipated through end 43 is heat sinked further through center post 27, insulative material 29, housing '25, and eventually into container wall 21. The heat dissipated through end 45 is heat sinked primarily through tip member 33 and then into the fluid within container 23. Provided tip member 33 remains subjected to the fluid, the heat created in element 31 is dissipated at a substantially equal rate through the above-described channels thereby maintaining the temperature of all members within sensor 13 approximately the same. However, when the fluid level drops below tip member 33, as illustrated in FIG. 4, an imbalance to this rate of dissipation is created. This unequal rate occurs primarily because the fluid, which previously served as a heat sink for the heat generated in end 45, is now absent. However, to further assure this imbalance during a low fluid level, it is preferred that the overall volume of center post 27 be substantially greater than the corresponding volume of tip member 33. It is also additionally preferred that the coefficient of thermal conductivity of center post 27 be larger than that of tip member 33, but this is not necessarily required provided a substantial difference of volumes between these two members exists. In the particular embodiment, the tip member comprised of Rodar has a coefiicient of thermal conductivity of approximately 12.0 BTU/(hr.) (sq. ft.) (F per ft.) while that of center post 27 which is preferably of steel or similar composition, ranges between 25 and 40 BTU/(hr.) (sq. ft.) (F per ft.).

As described, the absence of fluid now causes end 45 to become substantially warmer than end 43. This temperature difference in turn causes bimetallic member 49 to become warmer than bimetallic member 47 which results in an unequal amount of deflection by metallic member 49 to therefore upwardly deflect and engage member 4'7. When these two members engage (as shown in FIG. 4) electrical current from center post 27 through first opposing end 43 is permitted to by-pass resistive material 51 and pass directly to second opposing end 45 via the engaged bimetallic members 47 and 49 because the combined resistance of members 47 and 49 is effectively zero, as previously described. The current then returns to bulb 19 through tip member 33 and housing 25 where it now is at a sufficient level to actuate the bulb. This in turn indicates to an operator that the fluidlevel of container 23 is below tip member 33.

A unique feature of apparatus is that once bimetallic members 47 and 49 are engaged they will remain continuously so. This is achieved because the free end of bimetallic member 49 is substantially smaller than that of member 47. (This embodiment better illustrated in FIG. 5). The narrowed end of member 49 provides a substantially reduced path of current flow'in comparison to that provided by member 47. The electrical current through this circuit and thereby through member 49 causes member 49 to become substantially warmer than member 47. The increased heat in turn affects the thermal deflection characteristic of member 49 to the extent that it will now remain continuously against member 47 and thereby assure a steady high current flow to indicating means 119.

Another embodiment of the present invention is illustrated in FIG. 6 wherein a different means for assuring a steady increased current to indicating means 19 is shown. Attached to bimetallic member 49 is a helically wound electrically conductive wire 59 which has a terminal end 61 interspaced between bimetallic members 47 and 49. In operation, when fluid drops below tip 33, members 47 and 49 move toward engagement as previ ously described. However, rather than the two bimetalv lic members engaging, terminal end 61 engages member 47, thereby including helical wire 59 in the newly formed circuit. Electrical current therefore flows from spaced apart portion 43 to bimetallic member 47, wire 59, bimetallic member 49, spaced apart portion 45, and so on. Helical wire 59 now acts as a heater means, providing an additional source of heat to bimetallic member 49. As in the situation described in FIG. 5, this additional heat assures continual upward deflection (and thereby engagement between end 61 and member 47) of bimetallic member 49. Practically any electrically conductive material issuitable for wire 59 provided it also possesses the required thermal conductor properties. A preferred material for wire 59 is copper. To assure that bimetallic member 49 does-not directly engage member 47 and thereby electrically short out wire 59, a pad 63 of insulative material is affixed thereto.

Still another embodiment of a means for assuring continual engagement between bimetallic members 47 and 49 is illustrated in FIG. 7. Here an electrically conductive wire 65 is spirally wound about a portion of bimetallic member 49. Wire 65 also provides a means for interconnecting spaced apart portion with housing 25 as there is now utilized a different tip member 33. This new tip has a thermally conductive portion 66 and a portion of insulative material 67. A preferable material for portion 66 is copper while material 67 is preferably of plastic or similar material. Wire 65 serves a similar function to that of wire 59 in FIG. 6 by providng an additional heat source to bimetallic member 49 and thereby assuring continued engagement between the two members, 47 and 49.

As can be readily understood with the embodiment as shown it is essential that tip 33 be electrically insulated from housing 25. Were this not so, electrical current would by-pass wire 65 and flow directly to housing 25. The embodiment as shown in FIG. 7 provides an additional desirable feature of being substantially more rugged than the embodiment employing the relatively thin tip 33. Tip 33' is partially recessed within the end of housing 25 and also substantially thicker than tip 33. It is to be remembered, however, that the embodiments as shown in FIGS. 5 and 6 could be incorporated within tip 33' with only one minor alteration necessary providing a small interconnecting wire or similar electrical connection means between spaced apart portion 45 and housing 25.

To adequately achieve the degree of deflection re quired in the operation of the sensors illustrated, similar bimetals must be used for each of members 47 and 49. More specifically, a bimetal utilized successfully in sensor 13 is Chace 2400 bimetal, manufactured by the W. M. Chace Company of Detroit, Mich, a subsidiary of the previously mentioned W. B. Driver Company. Chace 2400 bimetal has a high expanding side (illustrated as high expanding layer 53 in FIG. 4) consisting essentially of about 22 percent by weight nickel, 3 percent by weight chromium, with the remainder iron, and a low expanding side (illustrated as low expanding layer 55 in FIG. 4) consisting essentially of 36 percent to 42 percent nickel with the remainder iron. An additional newly available bimetal also found suitable for use in sensor 113 is one produced by the W. M. Chace Company having a high expanding side consisting essentially of 22 percent nickel, 3 percent chromium, with the balance iron, and a low expanding side consisting essen tially 30% to 35% nickel with the remainder iron. The high expanding side of the bimetal has a first coefficient of thermal expansion of from 0 F to F of at least 7.0 X 106 per F and a second coefficient of thermal expansion lower than the first over a temperature range from 150 F to 600 F. The low expanding side of the bimetal has a first coefficient of expansion ranging from about 1.4 X 10 per F to about 6.0 X 10' per F over a temperature range of 0 F to 150 F and a second coefficient of expansion of at least 7.0 X 10 per F over a temperature range from about 400 F to 600 F. This particular bimetal reduces many of the stresses found in prior art bimetals and results in improved overall operating conditions, especially in the higher temperature ranges. Depending on the configuration used for each of the bimetallic members, as wellas the initial spacing between these members and the temperature difference required to cause their engaging, other bimetallic materials can be utilized successfully in this invention. For practical reasons however, bimetallic materials having operating characteristics substantially similar to those described are preferred.

In addition to providing means whereby a visual indication is given when the fluid within container 23 is below a certain level (in FIG. ll), apparatus 10 can be modified to perform other functions by relatively simple alterations to circuit 11, such as energizing other circuits, or to operate other mechanisms such as audible signals, valving arrangements and the like. For example, circuit 11 can be modified to include a means for actuating a valving arrangement in a boiler to thereby either shut down a burner or to open a valve and permit more fluid to enter the container, depending on the pre-established fluid level setting.

Besides this particular application, apparatus may be also used in other situations in which the fluids to be detected vary in temperature throughout their cycles of operation. Primary examples of such situations are found in the several containers of fluids utilized in the operation of automobiles. Sensor device 13 could easily be inserted into an automobiles brake fluid housing, radiator side wall, or the various housings for the transmission fluid, engine oil, power steering fluid, differential fluid, or even the windshield washer fluid, with the automobiles electrical circuitry readily able to substitute for circuit 11.

Thus there has been provided an apparatus for detecting the presence or absence of fluid at a predetermined level within a container. Unique features of this apparatus, which include temperature compensation means for varying fluid temperatures and sequentially actuated current indicating means, have also been provided.

While there has been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

What is claimed is:

1. In a sensor device comprising a housing member defining a chamber, a tip member adapted for being exposed to a fluid, said tip member secured to said housing and forming a closure for said chamber and to prevent fluid entrance into said chamber, a heat and electrical conductive member within said chamber having a greater heat transfer capability than said tip member, an electrically resistive heater means within said chamber having first and second spaced apart portions, said first portion in heat and electrical conductive relationship to said heat conductive member within said chamber, said second portion in heat conductive relationship to said tip member, and first and second electrically conductive heat responsive means having substantially similar characteristics of thermal deflection, said first and second heat responsive means in heat and electrical conductive relationship to said first and second spaced apart portions, respectively, and each having a free end adapted for mutual engagement only when the temperature difference between said first and second spaced apart portions of said heater means exceeds a predetermined level, said temperature difference resulting from a difference in rates of heat transfer of said heat conductive member and said tip member, the improvement comprising:

providing a secondary heater means within said sensor device for heating said second heat responsive means to provide continuous electrical connection between said first heat responsive means and said second spaced apart portion of said heater means when said temperature difference between said first and second spaced apart portions of said heater means exceeds said predetermined level.

2. The improvement according to claim 1 wherein said secondary heater means is provided by substantially reducing the cross-sectional area of the free end of said second heat responsive means whereby electrical current passing through said second heat responsive means will maintain said second heat responsive means at a temperature substantially warmer than said first heat responsive means.

3. The improvement according to claim 1 wherein said secondary heater means comprises an electrically conductive member positioned substantially adjacent saidsecond heat responsive means for engaging said free end of said first heat responsive means, said electrically conductive member adapted for transmitting heat to said second heat responsive means upon the passage of electrical current therethrough whereby said second heat responsive means will be maintained at a temperature substantially higher than said first heat responsive means.

4. The improvement according to claim 1 wherein said secondary heater means comprises an electrically conductive member positioned substantially around said second heat responsive means, said electrically conductive member adapted for transmitting heat to said second heat responsive means upon the passage of electrical current therethrough whereby said second heat responsive means will be maintained at a temperature substantially higher than said firstheat responsive means.

5. The improvement according to claim 3 wherein said electrically conductive member is comprised of copper.

6. The improvement according to claim 3 wherein said electrically conductive member is affixed to said second heat responsive means.

7. The improvement according to claim 4 wherein said electrically conductive member is comprised of copper. 

1. In a sensor device comprising a housing member defining a chamber, a tip member adapted for being exposed to a fluid, said tip member secured to said housing and forming a closure for said chamber and to prevent fluid entrance into said chamber, a heat and electrical conductive member within said chamber having a greater heat transfer capability than said tip member, an electrically resistive heater means within said chamber having first and second spaced apart portions, said first portion in heat and electrical conductive relationship to said heat conductive member within said chamber, said second portion in heat conductive relationship to said tip member, and first and second electrically conductive heat responsive means having substantially similar characteristics of thermal deflection, said first and second heat responsive means in heat and electrical conductive relationship to said first and second spaced apart portions, respectively, and each having a free end adapted for mutual engagement only when the temperature difference between said first and second spaced apart portions of said heater means exceeds a predetermined level, said temperature difference resulting from a difference in rates of heat transfer of said heat conductive member and said tip member, the improvement comprising: providing a secondary heater means within said sensor device for heating said second heat responsive means to provide continuous electrical connection between said first heat responsive means and said second spaced apart portion of said heater means when said temperature difference between said first and second spaced apart portions of said heater means exceeds said predetermined level.
 2. The improvement according to claim 1 wherein said secondary heater means is provided by substantially reducing the cross-sectional area of the free end of said second heat responsive means whereby electrical current passing through said second heat responsive means will maintain said second heat responsive means at a temperature substantially warmer than said first heat responsive means.
 3. The improvement according to claim 1 wherein said secondary heater means comprises an electrically conductive member positioned substantially adjacent said second heat responsive means for engaging said free end of said first heat responsive means, said electrically conductive member adapted for transmitting heat to said second heat responsive means upon the passage of electrical current therethrough whereby said second heat responsive means will be maintained at a temperature substantially higher than said first heat responsive means.
 4. The improvement according to claim 1 wherein said secondary heater means comprises an electrically conductive member positioned substantially around said second heat responsive means, said electrically conductive member adapted for transmitting heat to said second heat responsive means upon the passage of electrical current therethrough whereby said second heat responsive means will be maintained at a temperature substantially higher than said first heat responsive means.
 5. The improvement according to claim 3 wherein said electrically conductive member is comprised of copper.
 6. The improvement according to claim 3 wherein said electrically conductive member is affixed to said second heat responsive means.
 7. The improvement according to claim 4 wherein said electrically conductive member is comprised of copper. 